1. Technical Field
The embodiments described herein generally relate to motorized window coverings, and more particular to reducing noise and vibrations created by a motorized window covering.
2. Related Art
A problem with conventional motorized window coverings is transmission of vibrations induced in the motor, in particular “solidborne” transmission of vibrations. These vibrations can create operational problems as well as unacceptable noise levels. Typically, it is very important to reduce the noise emitted by such devices. For example, the emitted noise should be below 50 decibels.
The motor and other mechanical accessories of such motorized window coverings are usually included in a headrail, made of a metal sheet, such as steel or aluminium. Such a conventional headrail is often neither closed nor rigid. The transmission of vibrations from the motor to the headrail may activate vibration resonant modes of the headrail or at least will allow the radiation of vibrations upon the whole headrail surface with a strong amplification effect.
Consequently, damping accessories that provide viscoelastic suspension and/or viscoelastic transmission are often used with such devices to minimize the solidborne transmission. For example, the Australian patent application 2008100304 discloses a motorized shade assembly. A vibration-absorbing member is made of a buffering, flexible material and includes a central hole clamping the motor. The outer periphery of this member is pressed against the inner periphery of the headrail.
The US patent application 2009/0000749 discloses a drive unit for a Venetian blind or the like. The drive unit includes an electric motor, one or two gear units, and two output shafts. The motor casing is made with components, isolating coating, and damping plugs that provide acoustical damping and uncoupling and that are shaped to be insertable into the headrail.
EP 1 321 623 discloses a mounting apparatus for an electromotor installed in a U-shaped headrail including flexible vibration-damping bodies attached on the ends of mounting feet provided on the electromotor. A U-shaped clip is attached around the headrail between the two mounting feet and includes a clamping device that allows exerting a pressure on the electromotor.
It is then common to include vibration-damping bodies around a drive unit before inserting it in a window covering headrail. It should be noted that a conventional horizontal headrail is usually U-shaped. Accordingly, the drive unit, with vibration damping bodies, may be inserted in the headrail either laterally or vertically.
A problem with conventional damping suspension devices, such as those disclosed in the patents and patent applications discussed above is that they require a certain amount of stress or strain between the drive unit and the headrail to operate properly. In other words, if the damping devices are too lose when the drive unit is installed in the headrail, then they cannot provide adequate dampening; however, when the damping devices are sized to achieve the necessary stress or strain, then a certain amount of friction is created that makes it difficult to move the drive unit inside the headrail. On the other hand, if the friction is reduced, then the damping devices may not adequately dampen vibrations, the drive unit may not be adequately stabilized within the headrail, or both.
For example, in AU 2008100304 the interface between the vibration-absorbing member and the housing is quite small because of the circular configuration of ribs, which creates only tangential contact, and there are large gaps between the housing and most of the member in order to reduce friction. Axial holes in some of the ribs may further diminish the friction. But four screws traversing the headrail are needed to secure the drive unit in the housing.
In US 2009/0000749, a provision is made for leaving room between the isolating coatings and the headrail and the same considerations apply to damping plugs. But how the drive unit is kept tight into the headrail is not addressed, nor is it clear from the disclosure.
In EP 1 321 623 a means to secure the clip by exerting a pressure on the motor with an appropriate tool is disclosed. The clip tightens the headrail and compresses the vibration-damping bodies to provide the necessary stress or strain while allowing the drive unit to move within the headrail when the external clip is not in place. But the aesthetic result when the clip is installed is poor.